Rechargeable lithium-ion batteries are widely used for portable electronics because lithium is the lightest and most electropositive element, a combination of properties that are important for high energy density. Such batteries can store more energy than Pb-acid, Ni—Cd, and NiMH batteries, and they have long shelf and cycle lives. Because of this, there is a significant market centered on lithium-intercalation batteries. There are, however, several drawbacks associated with commercially available Li-ion batteries, which can pose safety hazards due to dendritic growth of Li metal onto graphite negative electrodes having the potential to produce an internal short. Moreover, the organic liquid electrolytes employed are flammable, and can produce toxic hydrofluoric acid when exposed to water. A solid-state battery that does not contain liquid electrolyte and does not form metallic lithium is desirable.
An additional drawback of present Li-ion batteries that prohibits widespread adoption in the electric and hybrid electric vehicle market is insufficient power density. The principal challenge to achieving high power densities in Li-ion batteries is increasing the rates of charge and discharge. One solution which will provide higher power density by increasing these rates is to utilize a three-dimensional Li-ion cell architecture having electrically isolated interpenetrating electrodes. Such an arrangement decreases the characteristic transport lengths of Li-ions moving in and between the electrodes, and can also dramatically increase the interfacial surface area between the electrodes. These benefits are demonstrated by the following relationship for power density.
      Power    ⁢                  ⁢    Density    ∝            Voltage      ×      Lithium      ⁢                          ⁢      ion      ⁢                          ⁢      conductivity      ×      Surface      ⁢                          ⁢      area              Lithium      ⁢                          ⁢      ion      ⁢                          ⁢      transport      ⁢                          ⁢      length      
Fabrication of a three-dimensional cell having high interfacial surface areas and short characteristic diffusion lengths requires three-dimensional electrodes having irregular surfaces. Coating such irregular shaped three-dimensional electrodes with a material that is electrically insulating as well as Li-ion conducting on the nanoscale is challenging.